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OCT111905 


Sewage  Purification  Plants 


By  J.W.  Alvord,  M.W.  S.  E. 


From  the  JOURNAL  OF  THE  WESTERN  SOCIETY  OF  ENGINEERS 

APRIL,  1902 


Joifrnal  of  the 

Western  Society  of  Engineers. 

VOL.  VII.  APRIL,   1902.  NO.  2. 

CXLII. 

SEWAGE  PURIFICATION  PLANTS.* 

JOHN  W.  ALVORD,  M.  W.  S.  E. 
Read  February  5,  790,2. 

The  literature  of  sewage  purification  contains  very  much  that  is 
theoretical  rather  than  practical.  It  also  contains  a  good  deal  that 
has  emanated  from  the  laboratory  rather  than  from  actual  practice. 
We  have  elaborate  reports  by  eminent  commissions  upon  miniature 
experimental  plants,  and  the  subject  loaded  with  the  literature  of 
proprietary  claims  and  patented  processes,  the  authors  of  which  are 
quite  lawless  as  to  exact  statement  of  fact.  These  reasons  have 
rendered  it  very  difficult  for  the  student  or  layman  to  form  any  ade- 
quate conception  of  the  advancement  in  this  branch  of  engineering. 

Added  to  the  difficulties  above  enumerated,  of  recent  years  there 
has  been  a  remarkable  advancement  in  our  understanding  of  primary 
principles  involved.  An  advance  which  has  rendered  necessary  the 
revisions  of  many  excellent  and  well  written  volumes  upon  this  sub- 
ject by  eminent  authors,  and  published  as  recently  as  within  four  or 
five  years. 

The  subject  of  purification  of  sewage  has  interested  not  only  the 
sanitary  engineer,  but  also  the  medical  profession,  the  chemist,  the 
bacteriologist  and  the  municipal  expert.  The  result  of  this  has  been 
that  the  language  of  this  specialty  has  become  replete  with  technical 
terms,  drawn  from  these  various  professions,  which  cause  it  to  be 
sometimes  rather  unintelligible.  Moreover,  as  is  the  case  with  every 
art  which  is  in  a  rapid  state  of  advancement,  new  theories  are  con- 
stantly being  propounded,  so  that  the  observer  is  often  perplexed  in 
his  attempt  to  decide  just  how  much  of  the  art  is  safely  or  surely 
determined,  and  just  how  much  is  still  in  a  theoretical  stage. 

Sewage  purification  plants  labor  under  the  difficulty  that  skilled 
expert  supervision  is  fully  as  necessary  in  their  operation  as  in  their 

NOTE.  After  the  presentation  of  the  paper,  Mr.  Alvord  informally  described 
about  sixty  stereopticon  views  of  Sewage  Purification  Plants,  completed  or  under 
construction,  only  a  portion  of  which  are  here  represented  with  brief  description. 


137639 


114 


Alvord — Sewage  Purification  Plants. 


design  and  construction.  This  is  a  condition  that  has  not  been 
recognized  by  the  public  at  large  and  is  only  beginning  to  be  appre- 
hended by  sanitary  engineers  themselves.  Sewage  purification 
works  return  no  revenue  for  the  investment,  and  therefore  do  not 


Alvord — Sewage  Purification  Plants.  115 

enjoy  the  popularity  for  municipal  purposes  that  a  good  paying 
water  works  plant  always  does.  It  is  but  natural,  therefore,  that 
those  municipalities  that  have  been  driven  to  adopt  such  plants, 
either  by  due  process  of  law  or  by  threats  of  legal  proceedings,  find 
themselves  unwilling  or  unable  to  properly  maintain  the  works 
after  they  are  constructed.  And  after  a  few  years,  during  which  the 
expenses  of  operation  are  cut  down  again  and  again,  the  plant 
naturally  fails  to  give  the  expected  results  and  as  a  consequence  is 
condemned  as  inefficient  in  design.  Especially  was  this  the  case  in 
former  years  when  the  expenses  of  operation  were  so  very  great. 
The  newer  and  more  recent  biological  processes,  connected  with 
automatic  operating  devices,  it  is  hoped  will  somewhat  escape  this 
difficulty.  Still  it  is  true,  so  far,  that  the  necessity  for  skilled 
supervision  is  not  yet  obviated. 

PRINCIPLES  INVOLVED  IN  PRESENT  PRACTICE. 

The  purification  of  sewage  as  now  practiced  most  sucessfully  re- 
quires that  the  process  be  divided  into  two  stages : 

In  the  first  stage  there  is  the  necessity  of  eliminating  all  of  the 
greater  portion  of  the  particles  of  suspended  organic  matter  con- 
tained in  the  liquid.  This  is  accomplished  more  or  less  success- 
fully by  screening,  sedimentation,  chemical  purification,  roughing 
filters,  bacteria  beds  and  the  septic  tank.  At  the  present  time  the 
septic  tank  is  generally  considered  to  be  the  most  economical  and 
efficient  means  of  accomplishing  the  first  stage  of  purification. 

The  second  stage  of  purification  consists  of  removing  the  more 
finely  suspended  residue  and  the  impurities  in  solution.  There  are 
many  ways  of  accomplishing  this,  known  by  different  names,  but 
the  general  principle  underlying  them  all  is  that  the  liquid  to  be 
purified  must  be  brought  into  contact  by  wide  diffusion  at  innum- 
erable points  with  certain  forms  of  nitrifying  bacteria  in  the  pres- 
ence of  a  sufficient  supply  of  oxygen  and  retained  under  such  con- 
ditions a  proper  length  of  time  for  complete  chemical  change  to  be 
accomplished ;  this  properly  done,  the  liquid  is  found  to  be  purified. 
Most  of  the  methods  by  which  this  principle  is  practically  applied 
involve  intermittency  of  application  of  the  liquid  to  the  filter  and 
its  alternating  areation.  This  second  stage  involves  processes  com- 
monly known  as  broad  irrigation,  intermittent  filtration,  bacterial 
contact  beds,  filters  with  forced  areation  and  continuous  filters. 

Sewage  purification  has  had  its  origin  and  greatest  development 
in  England,  where  crowded  populations  located  on  insufficient  water 
sheds  gave  rise  to  an  incredible  nuisance  which  would  seem  intoler- 
able in  our  own  country.  England  has  for  forty  years  past 
wrestled  with  the  sewage  problem,  and  it  is  safe  to  say  that  over 
one-half  of  the  sewage  of  the  United  Kingdom  today  passes  through 


116 


Alvord — Sezuage  Purification  Plants, 


^A^/^//;y.''^;-wv>.\\.  ,  ••"'  r-i 

'•  -%.;.///x^~ '  //^"ffim'fiR^ 


some  form  of  attempted  purification.  It  is  but  natural  that 
England  should  have  kept  in  the  lead  in  this  problem,  and  its  most 
interesting  recent  developments  have  found  their  greatest  apprecia- 
tion in  that  country. 

THE  SEPTIC  TANK. 

Both  in  this  country  and  in  England  in  a  number  of  instances 
reservoirs  have  been  built  prior  to  1894  and  operated  as  septic 
tanks  without  attracting  general  attention.  The  installation  at 


Alvord — Seivage  Purification   Tanks.  \  17 

Exeter,  England,  in  that  year  was  the  first  plant  to  attract  wide 
notice,  although  it  is  interesting  to  know  that  a  member  of  this 
Society  constructed  a  true  septic  tank  at  Urbana,  in  this  state, 
simultaneously  with  the  Exeter  tank. 

Broad  patents  have  been  issued  to  the  promoters  of  English 
tanks  in  this  country,  covering  the  principle  of  light  and  air  tight 
tanks  with  submerged  inlet  and  outlet,  but  it  is  significant  that  the 
owners  of  these  patents  have  never  yet  been  willing  to  test  their 
validity  in  court,  and  it  is  evident  that  should  they  do  so,  the 
claims  of  many  prior  installations  might  seriously  vitiate  their 
value.  For  this  reason  sanitary  engineers  are  everywhere  install- 
ing tanks  of  their  own  design.  It  has  been  shown  quite  clearly 


General  view  Intermittent  filtration  beds,  Lake  Forest  Plant,  ^  of  an  acre. 
Rate  of  flow,  300,000  gallons  per  acre  per  day,  and  upward. 

that  neither  the  exclusion  of  light  or  air  nor  the  submergence  of 
the  inlet  or  outlet  is  necessary  for  the  development  of  successful 
septic  action.  Many  engineers  prefer  a  form  where  these  require- 
ments are  entirely  neglected  as  giving  the  most  satisfactory  results; 
the  ferment  or  septic  action  appears  to  go  on  in  such  tanks  quite 
rapidly  and  the  suspended  matters  in  the  sewage  are  dissolved  as 
in  air  and  light  tight  tanks. 

The  septic  tank  is  not  a  complete  system  of  purification  in  itself; 
only  under  the  most  favorable  circumstances  does  it  give  effluents 
which  are  inoffensive.  Generally  the  average  effluent  is  both 
offensive  and  liable  to  cause  nuisance,  but  the  process  effects  one 
great  change  in  the  sewage — it  breaks  down  the  suspended  mat- 


118  Alvord — Sezvage  Purification,  Plants. 

«T 

ter,  some  of  which  disappears  in  the  form  of  inoffensive  gas,  while 
another  and  larger  portion  is  dissolved  into  solution.  This  is  ac- 
complished by  a  species  of  bacterial  fermentation  within  the  tank, 
and  when  the  fermentation  period  is  properly  adjusted,  and  not  too 
long  prolonged,  the  effluent  will  be  found  tolerably  free  from  sus- 
pended matter  and  in  a  condition  when  it  is  most  easily  oxidized 
by  further  filtration.  The  importance  of  this  change  in  the  char- 
acter of  the  sewage  from  an  economical  standpoint  is  much  greater 
than  would  be  first  perceived,  for  it  is  this  first  stage  of  purifica- 
tion that  has  always  proved  to  be  the  most  difficult  one.  Chemical 
precipitation,  with  all  its  expensive  machinery,  was  invented  for 
this  purpose,  but  it  does  not  accomplish  what  the  septic  tank  ac- 


View  of  Tank  Building  and  Filter  beds,  Lake  Forest.     10  Filter  beds,   3,200  sq. 
ft.    each,  receive  a  dose  of  about  8,000  gallons   once  in  10  or  12  hours. 

complishes  in  that  it  leaves  the  sludge  problem  unsolved  and  pro- 
vides an  effluent  so  loaded  with  disinfectant  that  it  is  not  easily  oxi- 
dized. Intermittent  filtration  alone  has  found  its  greatest  difficulty 
in  dealing  with  the  suspended  matters  carried  in  the  raw  sewage, 
which,  if  turned  upon  the  beds  without  preliminary  treatment, 
rapidly  forms  a  film  upon  their  surface;  this  impervious  crust 
would  very  soon  render  them  useless  if  not  removed  from  time  to 
time.  The  raking  off  of  this  surface  film  and  disposing  of  it  effec- 
tively, in  order  to  keep  the  beds  up  to  their  rated  capacity,  has 
always  caused  the  most  serious  expense  connected  with  intermit- 
tent filtration,  and  although  an  efficient  supervision  should  keep 
the  beds  well  cleaned,  it  is  evident  that  a  large  portion  of  the  time 


Alvord — Sewage  Purification  Plants.  119 

their  rate  of  filtration  will  only  be  a  portion  of  full  capacity  of  clean 
beds.  This  leads  to  the  necessity  for  an  increased  area,  which  in- 
volves increased  outlay. 

Effluents  from  a  septic  tank  which  is  doing  its  work  properly 
may  be  delivered  upon  an  intermittent  filtration  bed  for  many 
weeks  at  a  time  at  high  rates  of  flow,  with  apparently  but  the 
slightest  clogging — allowing  a  very  much  smaller  area  of  sand  to 
accomplish  the  work  than  would  be  the  case  if  the  raw  sewage 
were  turned  upon  the  beds  direct.  The  same  general  fact  may  be 
said  of  broad  irrigation,  and  it  has  been  shown  that  bacteria  beds 
are  injured  by  having  too  large  quantities  of  suspended  matter 
passed  upon  them  during  long  intervals  of  time.  Effluents  from 
septic  tanks  that  are  being  properly  worked  seem  to  be  very 
easily  oxidized.  The  organic  matter  contained  is  largely  in  solu- 
tion and  in  such  a  condition  of  instability  that  it  is  ready  to  break 
down  into  its  constitutional  gases  without  difficulty.  Nitrification 
sets  in  promptly  and  the  passage  through  a  single  intermittent 
sand  filter  will  usually  leave  but  one  or  two  per  cent  of  organic 
matter  in  the  final  effluent.  The  economy,  therefore,  of  the  septic 
tank  is  not  alone  that  no  expensive  machinery  is  required,  or  a 
large  amount  of  labor  to  perform  its  function ;  nor  is  it  due  entirely 
to  the  fact  that  it  eliminates  into  harmless  gases  a  large  portion 
of  the  sludge  left  in  it,  but  it  is  also  essentially  in  the  fact  that  it 
enables  the  effluent  to  be  filtered  at  very  high  rates  of  flow  through 
small  areas  of  soil  or  compactly  constructed  contact  beds  occupy- 
ing but  little  space. 

NEW  THEORY  OF  SEPTIC  TANK  CONTROL. 

The  septic  tank  has  passed  through  the  period  of  doubt  and  dis- 
trust and  is  now  being  carried  along  on  the  popular  wave  of  en- 
thusiasm. It  has  come  to  pass  that  almost  any  one  thinks  he  can 
design  such  tanks,  although  he  may  only  have  read  of  them.  Ac- 
cepting the  English  dictum  that  the  sewage  should  rest  in  the  tank 
from  12  to  24  hours,  many  tanks  in  this  country  have  been  designed 
on  this  basis,  ignoring  the  fact  that  English  domestic  sewage  will 
often  average  about  four  times  the  strength  of  American  sewage,  and 
that  the  English  climate  is  quite  different  from  the  climate  in  this 
country.  The  writer  has  found  that  septic  tanks  are  not  to  be 
designed  on  haphazard  principles,  and  has  developed  a  theory  from 
four  years'  practical  experience  in  the  operation  of  such  tanks,  that 
the  particles  of  every  sewage  require  a  rest  or  fermentation  period 
within  the  tank  the  length  of  time  of  which  must  be  adapted  to 
their  temperature,  their  concentration,  their  character  and  the  vol- 
ume of  flow.  It  has  been  clearly  shown  that  if  this  fermentation 
period  is  unduly  prolonged  poisons  are  created  which  are  detri- 


120 


Alvord — Sewage  Purification  Plants, 


mental  to  the  life  and  activity  of  the  anerobic  bacteria.     Such  im- 
pairment of  their  vitality  reduces  their  activity  and  fills  the  tank 


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Alvord — Sewage  Purification  Plants,  121 

with  undecomposed  suspended  matter,  which  must  be  necessarily 
cleaned  out  quite  often  and  produces  an  effluent  which  it  is  difficult 
to  oxidize.  On  the  other  hand  too  short  a  fermentation  period  does 
not  effect  that  degree  of  purification  of  the  suspended  matter 
which  is  possible  and  allows  considerable  suspended  matter  to  be 
carried  over  onto  the  filters  to  their  detriment,  and  also  causes  the 
tank  to  fill  with  sludge.  The  severe  winter  temperature  of  the 
northern  states  has  been  found  to  retard  septic  action,  while  the 
heat  of  summer  accelerates  it.  This  is  a  difficulty  not  so  observ- 
able in  England,  where  a  warm,  even  climate  prevails,  and  it  is  for 


Interior  of  Septic  Tank  at  Lake  Forest.     In  foreground  lateral  trough 
for  combining  various  compartments.     In  background 
automatic  diversion  chamber. 

this  reason  that  we  prefer  housing  our  tanks  with  a  light  brick 
building  covered  by  a  felt  roof  which  shall  equalize  the  extremes  of 
climate. 

The  theory  of  a  proper  fermentation  period  requires  that  some 
adjustment  should  be  made  between  the  volume  of  sewage  flowing 
into  the  tank  and  the  capacity  of  the  tank  itself.  It  is  evident  that 
a  tank  designed  for  the  sewage  of  2,500  people,  and  which  receives 
the  first  year  of  its  work  the  sewage  from  only  500  people,  has  its 
fermentation  period  prolonged  many  times  more  than  its  designer 
intended.  It  is  evident,  too,  the  strength  of  the  sewage  may  be  in- 
creasing as  more  and  more  house  connections  are  made  with  the 
sewage  system,  so  that  from  receiving  a  small  quantity  of  thin, 
weak  sewage  when  first  put  into  operation,  in  the  course  of  two  or 


122  Alvord — Sewage  Purification  Plants. 

three  years  it  may  receive  its  maximum  volume  of  strongly  concen- 
trated liquid.  If  now  a  winter  of  severe  weather  intervenes,  retard- 
ing the  septic  action,  and  the  alternating  summer  heats  accelerate 
it,  further  complication  ensues,  and  the  perplexed  public  who  begin, 
at  times,  to  perceive  an  odor  around  the  building  and  note  that  it 
has  to  be  cleaned  every  month  or  so,  lose  faith  in  the  original 
enthusiasm  of  its  designer. 

EXPERIMENTS  ON  SEPTIC  TANKS. 

Early  experiments  with  coloring  matter  showed  that  with  wide  or 
deep  tanks  the  flow  of  sewage  through  the  tank  was  more  rapid 
through  a  certain  defined  zone,  and  that  in  this  zone  a  portion  of 
the  sewage  remained  in  the  tank  only  about  one-third  of  the  time 


Lake  Forest  Plant.       Automatic  device  for   rotating  contents   of  piversion 

Chamber  to  filtration  beds.     Operation  effected  by  rising  and  falling 

floats,  a  rolling  ball  and  syphons  operated  by  air  valves. 

that  would  be  denoted  by  the  ratio  of  the  volume  of  the  sewage 
flowing  daily,  to  the  capacity  of  the  tank.  It  was  felt  that  this  dif- 
ficulty should  be  overcome  so  far  as  possible  by  more  skillful  design. 
The  first  tank  our  firm  designed  was  proportioned  for  a  24-hour 
rest  or  fermentation  period  for  the  maximum  flow  of  sewage,  some- 
what on  the  principle  that  one  would  load  a  gun  so  full  of  shot  that 
something  would  get  killed.  The  result  was  that  with  minimum 
flow  an  average  fermentation  period  of  over  three  days  resulted, 
and  the  tank  did  not  work  well ;  probably  portions  of  the  suspended 
matters  remained  in  the  tank  for  weeks  and  it  gradually  filled. 


Alvord — Sezuage  Purification  Plants.  123 

After  much  study  we  temporarily  partitioned  off  portions  of  the  tank 
with  a  light  wood  partition  of  matched  board  in  such  a  manner  as 
both  to  reduced  its  effective  capacity  and  prevent  the  direct  flow 
from  inlet  to  outlet,  with  marked  improvement  resulting.  Again 
sections  of  the  tank  were  partitioned  off  and  the  direct  path  of  flow 
from  inlet  to  outlet  still  further  retarded.  Finally  a  result  was 
reached  in  which  the  septic  action  seemed  to  equal  the  rate  of  in- 
flow of  suspended  matter,  and  this  condition  was  maintained  for 
some  months  until  cold  weather  set  in,  when  the  tank  began  to 
slightly  fill  again.  About  this  time  Prof.  Talbot  called  our  atten- 
tion to  the  fact  that  the  fermentation  was  much  more  rapid  in  sum- 
mer than  in  winter,  and  it  began  to  be  seen  that  adjustment  in  ca- 
pacity for  varying  conditions  must  be  provided  for. 

The  problem  of  preventing  the  direct  zone  of  flow  between  inlet 
and  outlet  presented  the  greatest  difficulty  in  originating  new  de- 
signs, and  experiments  showed  that  no  arrangement  of  baffle  boards 
was  wholly  able  to  overcome  this  difficulty.  The  best  results  were 
found  to  be  obtained  when  the  entering  flow  was  subdivided  into 
several  separate  streams  in  parallel  compartments.  By  this  means 
the  rates  between  the  volume  entering  a  given  tank  and  its  total 
capacity  could  be  somewhat  equalized. 

NEW    DESIGN    OF    TANK. 

In  order  to  more  thoroughly  control  the  variations  caused  by 
increasing  volume,  temperature  and  concentration,  a  so-called  elas- 
tic tank  was  designed  for  the  City  of  Holland,  Mich.,  having  three 
long  compartments  which  could  be  operated  singly,  in  duplicate, 
or  in  triplicate,  or  continuously  as  one  long  tank.  This  form  has 
proved  to  be  capable  of  easy  adjustment  and  well  adapted  to  prac- 
tical conditions,  and  in  some  of  our  more  recent  tanks  five  com- 
partments of  varying  capacity  have  been  introduced,  which,  when 
worked  singly  or  in  combination,  allow  almost  any  considerable 
fraction  of  the  whole  capacity  to  be  utilized  for  the  time  being; 
this  also  equalizes  the  tendency  for  portions  of  the  suspended  mat- 
ter to  reach  the  outlet  too  early.  The  gates,  troughs  and  chambers 
by  which  this  manipulation  is  effected  are  simply  and  conveniently 
arranged,  and  render  anything  but  skilled  superintendence  unneces- 
sary. 

In  actual  practice,  it  is  believed  that  when  a  septic  tank  has  its 
fermentation  period  properly  adjusted  to  the  strength,  quantity  and 
temperature  of  the  sewage  flowing  into  it,  there  will  be  a  minimum 
deposit  of  undecomposed  matter  upon  the  bottom  of  the  tank,  un- 
less cellulose  or  mineral  matter  is  present  in  large  quantities.  If 
so,  these  should  be  removed  by  a  preliminary  chamber  as  much  as 
possible.  A  great  deal  of  misapprehension  exists  in  regard  to  the 


124 


Alvord — Seivage  Purification  Plants. 


Septic  Tank  at  Holland,  Michigan,  discharging  effluent  directly  into  Black  Lake; 

built  entirely  of  wood.       Liquid  Capacity,  00,000  gallons.       Cost,  $1,200. 

Completed  in  1900.     First  tank  using  compartment  system  of  control. 

ability  of  a  septic  tank  to  consume  the  intercepted  suspended  mat- 
ter. Statements  are  frequently  heard  that  this  is  almost  entirely 
consumed,  and  that  the  tank  will  proceed  for  years  without  any 
material  increase  in  deposits.  It  may  be  possible  that  this  is  true 
in  the  case  of  a  tank  whose  fermentation  period  is  exactly  adjusted 
and  constantly  watched,  but  so  far  as  our  experience  has  gone, 
and  we  now  have  some  sixteen  tanks  in  operation,  the  adjustment 
cannot  be  made  so  perfectly  but  that  it  is  necessary  to  clean  the 
tank  at  least  once  in  a  long  while;  therefore  provision  is  made  for 
flushing  pipes  from  the  bottom  of  the  tank,  by  which  excessive 
deposit  can  be  removed. 

It  is  believed  that  of  the  many  tanks  recently  designed  and  con- 
structed without  apparent  reference  to  the  relation  of  capacity  to 
flow,  in  some  few  of  them  happy  accident  has  produced  the  right 
proportions.  Such  tanks  are  naturally  pointed  to  with  pride  as 
being  very  successful,  but  as  time  goes  by,  if  this  theory  is  right, 
they  may  become  unsuccessful  through  changes  in  volume,  tempera- 
ture or  strength.  In  like  manner  some  unsuccessful  tanks  may 
become  successful  ones.  With  the  elastic  tanks  it  is  believed  no 
such  chances  must  be  taken,  and  the  designer,  who  should  always 
superintend  the  operation  of  his  plant  for  at  least  a  year  after  it  is 
put  in  operation,  will  be  enabled  by  simply  opening  or  closing  a 
few  valves  to  experiment  for  the  first  few  weeks  until  he  arrives 
at  the  proper  fermentation  period  for  the  particular  quantity  or 


Alvord — Se^vage  Purification  Plants. 


125 


quality  of  sewage  which  he  has  in  hand,  and  thereafter  by  equally 
simple  manipulation  keep  it  in  successful  operation  without  rapidly 
forming  deposits  or  passing  an  undue  amount  of  suspended  matter 
to  the  filters.  The  septic  tank  in  good  working  condition,  and 
which  is  not  being  overcrowded,  should  have  from  four  to  eight 
inches  of  thick  scum  over  its  entire  surface.  There  should  be  no 
objectionable  odor  perceived  within  the  building  when  standing  im- 
mediately on  the  compartments,  and  none  at  all  outside  the  build- 
ing. The  effluent  is  rarely  without  some  odor  and  in  appearance 
will  often  be  slightly  clouded,  but  the  proportion  of  suspended 
matter  in  it  should  not  be  large  if  the  tank  is  working  properly. 

CHEMICAL  PRECIPITATION. 

Of  chemical  purification,  as  a  method  of  eliminating  suspended 
matter  in  the  first  stage  of  sewage  purification,  it  is  sufficient  to  say 
that  with  the  exception  of  a  few  rare  cases  it  is  already  generally 
considered  as  out  of  date,  as  an  economical  and  efficient  process.  Of 
the  19  chemical  purification  plants  visited  by  the  writer  in  England 
in  1888,  only  two  could  be  properly  called  inoffensive  and  they 
were  but  recently  built.  Chemical  purification  has  been  humor- 
ously described  by  the  late  Col.  Waring  as  "A  method  by  which 
you  buy  chemicals  and  employ  labor  to  mix  them  with  the  sewage, 
settle  the  sewage  in  expensive  tanks,  press  the  sludge  thus  ob- 


Septic  Tank  at  Danville,  Ky.,  followed  by  intermittent  subsoil  filtration. 
Built  in  1901.     In  operation  since  September,  1901. 


126  Alvord — Sewage  Purification  Plants. 

tained  in  complicated  machinery  and  after  all  have  the  sewage  left 
on  your  hands,  without  having  purified  the  water  which  originally 
contained  it." 

The  writer  has  recently  noticed  an  account  of  a  chemical  purifi- 
cation plant  in  England  which  was  so  offensive  that  legal  proceed- 
ings were  brought  and  judgment  for  damages  obtained  on  account 
of  the  nuisance,  by  a  land  owner  who  resided  five  miles  away  from 
the  plant. 

The  enormous  expense  of  operating  chemical  purification  renders 
it  quite  certain  that  at  no  distant  day  the  largest  portion  of  the 
plants  of  this  character  will  be  replaced  by  the  septic  tank,  where 
the  same  work  is  accomplished  with  practically  no  operating  ex- 
pense. It  is  because  of  this  fact  that  we  see  the  present  en- 
thusiasm for  the  septic  process. 

THE  SECOND  STAGE  OF  SEWAGE  PURIFICATION. 

The  second  stage  of  sewage  purification,  by  which  the  organic 
matter,  which  is  largely  in  solution,  is  eliminated,  is  perhaps  better 
understood  in  practice  and  presents  less  difficulties  than  does  the 
first  stage,  already  considered. 

Broad  irrigation  and  intermittent  filtration  have  been  known  and 
practiced  for  many  years  and  much  data  and  information  exist  as  to 
their  details.  Their  chief  difficulties  have  arisen  from  the  accumu- 
lation of  suspended  matter  upon  the  surface  when  the  raw  sewage 
was  turned  directly  upon  the  land  and  the  large  areas  required  in 
consequence. 

In  England,  where  land  near  large  cities  is  enormously  expensive, 
they  have  endeavored  for  years  to  overcome  this  objection  by  im- 
provements in  chemical  precipitation  as  a  first  stage,  and  attention 
was  early  attracted  by  the  experiments  of  the  Massachusetts  State 
Board  of  Health,  which  showed  the  wonderful  effectiveness  of  fine 
gravels  in  oxidizing  the  impurities  of  the  sewage  which  dripped 
through  it.  As  a  result  of  further  experiments  along  this  line,  sani- 
tary engineers  there  developed  the  bacteria  and  contact  bed  as  a 
method  of  consuming  suspended  matter  as  well  as  oxidizating  or- 
ganic matter  in  solution. 

CONTACT  BEDS. 

The  early  English  experiments  on  contact  beds  were  summarized 
by  the  writer  in  a  paper  presented  to  this  Society  in  1898.  A  con- 
tact bed,  it  may  be  explained,  is  a  water  tight  tank  filled  with  fine  or 
coarse  particled  matter  and  into  which  the  sewage  is  regularly  filled, 
rests  for  a  few  hours  full  and  is  then  emptied.  An  interval  then 
ensues  in  which  the  air,  drawn  down  into  the  body  of  the  tank  by 
the  removal  of  the  liquid,  thoroughly  permeates  its  interstices  and 


Alvord — Sezvage  Purification  Plants, 


127 


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aerates  it ;  the  bacteria  which  swarm  over  every  particle  of  the  filter 
in  the  presence  of  such  effective  aeration  oxidizes  the  organic  im- 
purities of  each  liquid  dose  as  they  successfully  pass  through  the 
bed,  and  remove  a  large  portion  of  the  impurity. 

A  contact  bed,  as  has  been  remarked  by  the  writer  elsewhere,  re- 
sembles nothing  else  so  much  as  a  huge  lung.  The  filling  and 
emptying  of  the  liquid  in  the  contact  bed  corresponds  to  the  in- 
haling and  exhaling  of  a  breath,  and  as  the  indrawn  air  in  the  lung 
oxidizes  the  impurities  of  the  blood  through  the  thin  walls  of  its  tis- 
sue, so  does  the  entrained  air  and  bacteria  in  the  contact  bed  do  its 
work  upon  the  dissolved  impurities  in  the  sewage. 


128 


Alvord — Seivage  Purification  Plants. 


It  has  been  found  desirable  where  a  high  degree  of  purification 
is  desired  to  follow  one  contact  by  a  second  contact  in  a  bed  of 
finer  grain,  emptying  the  contents  of  one  bed  into  a  second  bed  at 
lower  grade,  and  if  necessary  the  process  can  be  repeated  a  third  time. 

Long  continued  trials  of  the  coarser  grain  bacteria  beds  dosed 


Alvord — Sewage  Purification  Plants.  129 

with  raw  sewage  only  partially  screened  as  a  first  stage  of  purifica- 
tion, have  given  rise  to  the  fear  that  they  are  liable  to  gradual  clog- 
ging with  suspended  matter,  and  require  to  be  cleaned  or  washed, 
and  perhaps  rehandled ;  that  this  is  positively  necessary  in  all  cases 
has  not  yet  been  fully  settled ;  but  if  it  is  found  to  be  the  case,  it 
is  a  question  as  to  whether  the  cost  would  not  be  much  less  than 
the  expense  of  labor  in  raking  intermittent  filtration  beds  upon 
which  the  raw  sewage  is  turned.  The  whole  question  of  the  best 
method  of  treating  suspended  matters  as  the  first  stage  has  been 
for  the  present  settled  in  favor  of  the  septic  tank,  as  has  been  al- 
ready shown,  and  the  proper  field  of  the  contact  bed  is  now  deemed 
to  be  the  second  stage  or  the  purification  of  matters  in  solution. 

For  the  second  stage,  the  contact  method  has  undoubted  advan- 
tages, especially  where  sufficient  area  of  sand  bed  is  not  available 
for  intermittent  filtration.  If  sand  beds  for  intermittent  filtration 
have  to  be  constructed,  contact  beds  will  almost  always  be  found 
to  be  more  economical.  But  if  the  sand  is  in  place  or  nearly  so  and 
of  the  right  grain,  and  land  is  not  too  dear,  intermittent  filtration 
will  generally  be  found  the  least  expensive.  Contact  beds  occupy 
much  less  area  for  a  given  capacity  than  do  sand  beds  for  intermit- 
tent filtration,  but  being  of  water  tight  construction  this  advantage 
is  sometimes  overcome  by  this  expense. 

Properly  operated,  intermittent  filtration  will  give  high  rate  of 
purification,  much  more  so  than  single  contact  beds,  but  double  con- 
tact beds  will  do  nearly  as  well  as  a  single  intermittent  filtration 
through  sand  of  the  proper  grain. 

The  degree  of  purification  to  be  attained  by  any  plant  is  always 
a  matter  of  local  consideration.  In  some  cases  it  is  only  necessary 
to  abate  a  nuisance,  in  others  a  water  supply  must  be  protected ; 
either  can  be  accomplished,  but  the  latter  requirements  will  cost 
more  to  attain  than  the  former. 

AUTOMATIC  CONTROLLING  DEVICES. 

With  the  advent  of  contact  beds  has  come  the  necessity  of  auto- 
matic control  of  the  filling  and  emptying  period.  The  regulation 
contact  beds  have  of  necessity  to  be  quite  even  and  regular,  and 
while  the  method  of  emptying  and  filling  by  hand  has  been  adopted 
in  some  cases,  automatic  devices  operated  by  the  rise  and  fall  of  the 
liquid  within  the  tank  have  become  popular  and  a  few  have  proved 
successful.  There  are  several  patent  devices  in  England  for  this 
purpose  and  several  in  this  country,  some  of  which  are  being  intro- 
duced at  a  number  of  places.  These  devices  will  undoubtedly  work 
a  great  revolution  in  the  care  and  management  of  sewage  disposal 
plants.  In  intermittent  filtration  practice  with  raw  sewage  it  has 
always  been  the  custom,  inasmuch  as  labor  was  necessary  for  raking 


******* 


130  Alvord — Se^vage  Purification  Plants. 

off  the  beds,  to  utilize  that  labor  in  rotating  the  flow  from  one  bed 
to  another,  but  with  the  advent  of  the  septic  tank  and  the  discon- 
tinuance of  the  frequent  rakings  has  also  come  the  demand  for  au- 
tomatic control  for  rotating  the  flow,  and  this  is  as  necessary  in  in- 
termittent filtration  as  it  is  in  single  or  double  contact  beds.  With 
the  successful  introduction  of  such  devices,  diverting  the  flow  from 
septic  tanks  to  secondary  treatment  by  filtration  in  rotation,  sewage 
disposal  plants  have  become  well  nigh  automatic,  requiring  little  or 
no  ordinary  labor,  and  a  minimum  of  skilled  supervision  so  far  as 
time  is  concerned.  Not  only  this,  but  automatic  devices  make  in- 
termittent filtration  more  efficient  than  ever  before  by  reason  of 


General  view  Septic  Tank  at  Princet'on,  111. 

Controlled  by  5-compartment  system.     Liquid  capacity,  60,000  gallons. 
Cost,   $3,500. 

the  regularity  by  which  the  process  proceeds,  and  the  independence 
which  results  from  a  disregard  of  certain  fixed  hours  of  labor.  It 
is  customary  to  operate  contact  beds  with  two  hours  resting  full, 
thirty  minutes  to  empty,  three  hours  resting  empty  to  aereate,  and 
thirty  minutes  or  so  to  fill,  thus  dividing  the  day  into  six-hour  cycles 
and  providing  for  four  fillings  per  day.  With  strong  sewage,  eight- 
hour  cycles  and  three  fillings  and  emptyings  per  day  are  sometimes 
best.  All  this  work  may  go  on  continuously  with  the  automatic 
devices  without  regard  to  night  or  day,  noon  hour  or  work  hour,  fair 
weather  or  storm,  and  this  regularity  is  found  to  be  very  desirable 
and  essential  to  the  economical  workings  of  the  plant,  for  by  its 


Alvord — SecL'age  Purification  Plants.  131 

means  the  greatest  possible  effectiveness  is  obtained  from  any  given 
contact  bed  or  filter. 

One  of  the  plants  designed  by  the  writer's  firm  which  was  put  in 


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operation  last  summer  has  been  working  automatically  ever  since. 
It  is  visited  for  a  few  minutes  twice  each  week  to  see  that  no  mali- 


132  Alvord — Sewage  Purification  Plants, 

cious  mischief  has  been  done  and  that  nothing  is  out  of  order.  On 
such  visits  the  attendant  notes  the  temperature,  quantity  of  sewage 
which  has  been  purified  since  his  last  visit  (obtained  by  reading  a 
counter  on  the  automatic  device),  and  notes  such  other  points  as  may 
be  interesting  or  necessary  in  regard  to  the  plant.  It  is  believed 
from  the  past  six  months'  experience  that  $100  per  annum  will 
cover  the  cost  of  maintenance  of  this  plant,  which  is  purifying  the 
sewage  of  about  2,000  people. 

COMPARISON    OF    COST. 

In  order  to  fully  appreciate  some  of  the  modifications  which 
have  been  brought  about  in  the  filtering  of  septic  tank  effluents,  it 
is  necessary  to  remember  that  the  Massachusetts  State  Board  of 
Health  experiments  have  shown  that  in  order  to  filter  raw  sewage 
successfully  upon  fine  sand  beds,  an  acre  of  bed  is  necessary  for 
each  16,000  to  20,000  gallons  of  sewage  per  day.  With  somewhat 
coarser  sand  from  30,000  to  40,000  gallons  per  day  of  raw  sewage 
can  be  filtered,  while  with  very  coarse  sand  there  is  a  possibility  of 
passing  from  100,000  to  150,000  gallons  per  day  if  the  beds  are 
kept  well  raked.  With  septic  tank  effluents  where  there  is  but 
little  suspended  matter  to  deal  with,  and  the  liquid  is  ripe  for  oxidiz- 
ation, even  with  quite  fine  sand  at  least  200,000  gallons  per  acre 
per  day  can  be  filtered,  with  coarser  sand,  350,000  gallons  would 
be  a  safe  allowance;  while  with  the  coarsest  and  most  desirable 
sand  at  least  500,000  gallons  per  acre  per  day  is  possible.  The 
difference  between  these  figures  is  this,  that  if  you  have  a  plant 
that  must  purify  the  sewage  of  2,500  people  by  the  older  method 
of  intermittent  filtration  alone,  you  would  require  (at  100  gallons 
per  capita)  not  less  than  seven  acres  of  sand  bed  for  medium  sized 
sand,  and  if  the  available  sand  was  quite  fine  this  would  become 
14  acres.  If  the  sand  had  to  be  brought  from  any  considerable 
distance  the  beds  would  cost  complete  not  less  than  $10,000  per 
acre,  or  from  $70,000  to  $140,000  for  the  plant.  Now,  consider- 
ing the  substitution  of  the  septic  tank  preliminary  to  the  filtration, 
and  yo.u  would  at  once  reduce  the  cost  for  filtration  area  to  about 
three-fourths  of  an  acre,  and  you  might  easily  afford  the  coarsest 
sand  brought  from  a  great  distance  for  the  beds,  which  even  then 
could  be  worked  at  a  rate  not  exceeding  300,000  gallons  per  acre 
per  day,  and  the  entire  plant  would  cost  not  more  than  $16,000, 
including  the  septic  tank.  Compare  this  with  the  $70,000  to 
$140,000  mentioned  before,  and  some  of  the  enormous  advantages 
of  the  later  processes  can  be  appreciated,  especially  in  unfavorable 
localities.  Not  only  in  first  cost,  but  also  in  operating  expenses, 
simple  intermittent  filtration  alone  would  cost  at  least  twice  if  not 
three  times  greater  than  that  necessary  for  the  septic-tank  installa- 


Alvord—Sezvage  Purification  Plants. 


133 


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tion.  Such  a  comparison  as  this  I  have  just  described  is  not  at 
all  uncommon,  and  is  simply  revolutionary  in  its  results.  It  per 
mits  cities  to  own  and  operate  sewage  purification  plants  to  whom 
it  has  been  heretofore  impossible.  It  allows  plants  to  be  built  in 
localities  where  every  advantage  is  lacking,  and  it  permits  the 
problem  to  be  brought  within  workable  limits  for  the  largest  cities 
of  this  country.  In  bacterial  contact  plants  the  results  are  still  more 


134  Alvord — Sezvage  Purification  Plants. 

favorable  as  to  the  rates  of  flow.  With  septic  tanks  effluents  most 
of  these  contact  bed  plants  are  worked  at  the  rate  of  500,000  to 
750000  gallons  per  acre  per  day,  with  the  same  rates  of  reduced 


Interior  of  Septic  Tank  at  Princeton,   111.,   before  admission  of  sewage. 
Initial  compartment  inlets  and  sludge  valves. 

cost  for  maintenance,  and  it  is  questionable  whether  a  rate  of 
1,000,000  gallons  per  acre  per  day  for  dilute  American  sewage  is 
not  fairly  practicable. 

Already  the  city  of  Manchester,  England,  has  under  way  a  proj- 
ect for  the  purification  of  the  sewage  on  these  new  principles,  cost- 
ing $1,150,000.  The  city  of  Leeds  will  soon  follow,  and  over  200 
projects  are  on  foot  for  cities  of  less  population  in  England  alone. 
We  shall  watch  these  experiments  on  so  large  a  scale  with  unusual 
interest. 

DISCUSSION. 

Mr.  Finley — How  high  are  those  beds  at  Lake  Forest  above 
Lake  Michigan  ? 

Mr.  Alvord — The  surfaces  of  the  beds  are  about  six  feet  above 
Lake  Michigan,  and  of  course  they  are  thoroughly  drained  by  a 


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136  Alvord — Sewage  Purification  Plants 

main  underdrain,  with  numerous  branches.  One  of  the  difficult 
problems  of  this  site  was  to  prevent  the  beds  from  being  injured 
by  the  wind  blowing  along  the  beach,  which  tends  to  fill  the  beds 
with  fine  sand,  so  that  they  become  flooded.  We  are  constructing 
a  very  high  board  fence,  which  we  think  will  prevent  this  trouble. 

Mr.  Francis  H.  Bainbiidge — I  would  like  to  ask  Mr.  Alvord  if 
these  sand  beds  ever  have  to  be  cleaned  or  replaced  when  used  for 
filtering  purposes? 

Mr.  Alvord — They  may  have  to  be  surface  cleaned,  but  not  re- 
placed. So  far  as  intermittent  filtration  has  been  known  and 
practiced  for  the  last  dozen  or  fifteen  years,  there  has  been  found 
to  be  no  necessity  for  replacing  the  sand  of  the  beds.  There  is 
necessity,  however,  of  loosening  the  surface  once  in  a  while,  which 
is  generally  done  by  raking  off  and  and  removing  the  surface  flake 
or  crust,  if  any;  with  the  septic  tank  effluent  the  raking  has  be- 
come very  much  less  burdensome. 

Mr.  Finley — Mr.  Alvord,  I  believe  you  said  that  the  plant  for 
Princeton  cost  $3,000,  with  a  population  of  4,000.  What  is  the 
cost  of  the  maintenance  of  that  plant  ? 

Mr.  Alvord — The  filter  beds  have  not  yet  been  constructed  in 
that  plant,  and  of  course  we  do  not  know  what  the  maintenance 
would  be.  In  our  Wauwatosa  plant,  judging  from  the  run  which 
it  has  had  so  far,  we  think  $100  a  year  would  be  a  very  ample 
figure  to  estimate  on,  and  that  is  providing  for  the  sewage  of  about 
2,000  people.  The  first  cost  of  that  plant  was  a  little  over  $5,000. 
The  first  cost  of  the  Lake  Forest  plant  was  $8,000.  The  total 
cost  of  the  Princeton  plant,  when  it  is  completed,  will  be  about 
$6,500. 

Mr.  Torrance — What  happens  to  those  sand  filters  during  the 
winter  months?  For  instance,  such  weather  as  we  had  yesterday. 

Mr.  Alvord — Sewage  in  process  of  dissolution  is  undergoing  a 
chemical  change,  which  gives  rise  to  heat,  and  that  heat  is  thrown 
out  into  the  sand  beds.  It  is  generally  sufficient  to  melt  them  if 
they  are  already  frozen.  It  keeps  the  interior  of  the  septic  tanks 
quite  warm.  In  fact,  the  men  completing  our  Lake  Forest  plant 
were  accustomed  to  eat  their  lunches  in  the  septic  tank,  after  it 
was  in  operation,  that  being  the  warmest  place  they  could  get. 
The  Lake  Forest  beds  were  quite  well  frozen  before  the  sewage 
was  turned  onto  them,  but  after  a  very  few  days  the  main  part  of 
the  frost,  which  perhaps  was  two  feet  thick,  disappeared.  The  ten- 
dency is  for  a  light  crust  of  ice  or  snow  to  form  on  the  top  of  the 
beds,  but  underneath  that  crust  the  filling  and  soaking-in  process 
is  going  on  all  the  time,  even  through  the  very  severely  cold 
weather. 

Prof.  A.  N.  Talbot — I  have  been  very  much  interested  in  Mr. 


Alvord — Selvage  Purification  Plants. 


137 


View  of  construction  of  Septic  Tank  at  Wauwatosa,  Wis. 
Framing  of  forms  for  concrete  work. 

Alvord's  presentation  of  the  details  of  the  purification  plants  which 
he  has  constructed,  and  he  has  certainly  had  very  valuable  experi- 
ence and  has  constructed  very  successful  plants.  As  he  has  stated, 
many  changes  in  ideas  concerning  methods  of  purification  have 
been  made  in  the  past  few  years,  and  while  a  great  deal  has  been 
learned  concerning  the  processes  of  purification,  many  matters  re- 
main unknown  or  are  yet  in  dispute.  It  would  not  be  strange,  then, 
if  I  should  differ  with  Mr.  Alvord  in  regard  to  some  details  of  the 
methods  to  be  used  in  such  purification  or  in  the  explanation  of  the 
action  of  processes,  and  of  the  principles  involved  in  this  purifica- 
tion. However,  it  does  not  seem  best  to  take  up*  this  matter  at  this 
time.  It  seems,  though,  that  the  question  of  the  use  of  terms  to 
be  employed  might  be  discussed  a  little.  In  a  subject  as  new  as 
this  it  is  not  strange  that  there  should  be  differences  in  the  use  of 
terms,  and  it  is  well  to  attempt  to  start  a  usage  which  will  be  sys- 
tematic and  not  misleading. 

It  has  seemed  to  me  wise  to  confine  the  use  of  the  term  "  con- 
tact bed"  to  those  beds  in  which  there  is  aerobic  action  in  the  pur- 
ification of  the  sewage ;  that  is,  to  those  beds  in  which  air  is  freely 
admitted  and  in  which  the  sewage  has  been  sufficiently  cleared  of 
organic  matter  in  suspension  to  permit  this  aerobic  action  to  take 
place.  In  a  paper  given  by  Mr.  Alvord  a  number  of  years  ago,  the 
coarse  bacteria  bed  was  described.  These  beds  were  filled  and 
emptied  in  much  the  same  way  as  the  ordinary  contact  bed,  except 
that  raw  sewage  (still  holding  the  suspended  organic  matter)  was 


138  Alvord — Sewage  Purification  Plants. 

applied.  Between  the  time  of  emptying  and  filling,  little  oppor- 
tunity was  given  for  air  to  reach  the  interior,  as  the  retained  organic 
matter  and  organic  growth  prevented  easy  access,  and  this  and  the 
quick  consumption  of  the  oxygen  reaching  the  interior  formed  con- 
ditions which  made  the  bacterial  action  mainly  anaerobic.  There 
was  then  little  effect  on  the  matter  in  solution,  and  the  effect  was 
similar  to  septic  action.  I  think  such  a  bed  should  retain  the 
name  "coarse  bacteria  bed,"  and  that  the  term  "contact  bed" 
should  be  confined  strictly  to  what  was  formerly  known  as  fine 
bacteria  beds.  The  contact  bed,  then,  takes  sewage  from  which 
most  of  the  suspended  matter  has  been  removed  by  some  process 
and  acts  upon  the  finely  divided  matter  and  upon  that  in  solution. 


Construction  of    Intermittent  Filter  Beds  at  Wauwatosa,  Wis. 
First  layer  of  gravel  being  spread  around  underdrains. 

Its  action  is  mainly  aerobic.  In  this  connection  it  maybe  said  that 
it  seems  to  me  that  the  purifying  action  of  such  beds  is  mainly 
during  the  time  in  which  the  sewage  is  held  in  the  bed. 

In  passing  it  may  be  added  that  coarse  bacteria  beds  which  were 
in  operation  at  Sutton,  England,  and  experimental  beds  at  Man- 
chester and  Leeds  have  proved  to  be  not  very  successful,  as  they 
became  clogged  and  had  to  be  cleaned. 

In  the  same  way  with  intermittent  filtration.  It  seems  to  me  the 
term  "  intermittent  filtration "  of  sewage  should  be  used  for  that 
process  where  the  sewage  is  applied  intermittently  and  is  distributed 
throughout  the  depth  of  the  bed  without  at  any  time  completely 
filling  it. 


Alvord — Sewage  Ptirificatton  Plants.  130 

As  Mr.  Alvord  knows,  I  have  also  objected  to  the  term  "fermen- 
tation "  or  "rest  period"  in  describing  the  capacity  of  septic  tanks. 
The  term  is  misleading  in  that  one  is  likely  to  think  that  the  sew- 
age actually  remains  in  the  tank  during  the  time  indicated.  Of 
course  the  matter  in  solution,  the  liquid  which  passes  through,  is 
changed  to  no  great  extent  in  the  passage  through  the  tank.  As 
stated  in  the  paper  given  before  this  Society  some  time  ago,  it 
seems  to  me  that  the  capacity  of  these  tanks  is  limited  or  governed 
by  the  area  of  the  surface,  and  by  the  time  taken  to  change  the 
organic  matter  in  suspension  which  is  left  behind  in  the  septic 
tank.  That  is  to  say,  if  the  flow  through  the  tank  is  slow  enough, 
there  will  be  a  subsidence  or  sedimentation  which  may  be  sufficient 


Construction  of  Automatic  Diversion  Chamber  at  Wauwatosa.Wis. 
Setting  the  syphons  in  the  bottom  of  the  chamber. 
Each  bed  has  an  independent  syphon  and  connection. 

to  retain  the  suspended  matter,  even  with  a  relatively  considerable 
flow,  but  this  retained  suspended  matter  must  be  allowed  consider- 
able time  for  the  operation  of  the  bacteria,  and  if  this  exposed  sur- 
face becomes  coated  over  by  other  organic  matter  before  the  bac- 
terial action  is  well  under  way,  as  would  be  the  case  where  the  tank 
is  too  small,  the  effective  action  of  the  tank  would  be  reduced,  and 
the  tank  would  fill  up  rapidly.  To  avoid  a  possible  misconception 
of  terms  like  "fermentation"  or  "rest  period,"  the  capacity  of  the 
tank  may  be  expressed  in  terms  of  the  number  of  hours'  flow  of 
sewage,  as,  for  example,  a  tank  of  cubic  capacity  equal  to  eight 
hours'  flow  of  sewage. 


140  Alvord — Sewage  Purification  Plants. 

Concerning  elastic  tanks,  it  should  be  stated  that  the  size  of 
tank  may  vary  within  considerable  limits  without  seeming  to  affect 
the  effluent.  For  example,  experiments  made  in  Leeds,  Eng. — not 
laboratory  tests,  but  on  tanks  of  250,000  gallons  capacity — showed 
very  little  difference  in  results  obtained  with  tank  capacities  of 
twelve  hours,  twenty-four  hours,  and  forty-eight  hours'  flow  of 
sewage.  This  of  course  was  strong  sewage. 

Mr.  Finley — This  question  of  sewage  purification  being  in  such 
a  condition  of  evolution,  I  have  wondered  whether  it  is  a  good  in- 
vestment for  a  village  to  spend  very  much  money  on  these  sys- 
tems. 

Mf.  Bainbridge — If  they  do  not  spend  the  money,  then  there 
will  be  no  further  evolution. 


Automatic  Ball  Controlled  Device  operating  six  intermittent  fil- 
tration  beds   at  Wauwatosa,  Wis.     Has  been    in 
successful  operation  since  September,  1901. 

Mr.  Potter — It  seems  to  me  the  best  thing  to  do  is  to  adopt  the 
best  method  now  available  and  then  when  improvements  are  made, 
incorporate  them  later.  Most  villages  are  compelled  to  take  some 
action  by  the  existence  of  serious  nuisance,  and  often  they  are 
driven  into  it,  by  threats  of  legal  proceedings. 

Mr.  Finley — If  I  remember  rightly,  the  City  of  Madison  put  in 
some  arrangement  for  the  treatment  of  sewage  which  was  not  very 
successful. 

Mr.  Alvord — They  let  a  contract  to  a  proprietary  company  for  a 
chemical  purification  plant,  with  a  guarantee,  which  was  not  sue- 


Alvord — Sezvage  Purification  Plants.  141 

cessful,  but  have  substituted  for  it  a  septic  tank  with  contact  beds 
designed  by  a  competent  sanitary  engineer,  which  I  think  is  doing 
very  well. 

Mr.  C.  D.  Hill — What  would  the  effect  be  to  lose  the  matte 
that  forms  on  the  surface  of  the  tank,  by  removal  of  the  baffle 
boards? 

Mr.  Alvord — Our  observation  has  been  that  baffle  boards  are 
not  absolutely  necessary  and  that  the  matte  will  stay  there,  even 
without  them,  and  in  so  far  as  it  is  a  question  of  whether  it  brings 
conflict  with  any  patent  claims,  we  have  decided,  in  one  of  our 
plants,  to  leave  the  baffle  boards  out  temporarily.  We  do  not 
always  do  that,  but  we  did  in  this  case. 


Distribution  of  Septic  Tank  effluent  upon  intermittent  filtration  beds, 

at  Wauwatosa,  Wis.     View  taken  4  minutes  after  discharge 

in  diversion  chamber.     Dose,  6,000  gallons. 

Mr.  Bainbridge — -What  is  the  action  of  the  matte  in  the  septic 
tank? 

Mr.  Alvord — There  forms  on  top  of  the  tank  a  scum,  which  con- 
sists of  the  residue  from  the  suspended  matte  in  the  sewage.  The 
particles  of  organic  matter  as  they  enter  the  tank  are  attacked  by 
the  bacteria  in  the  tank  and  certain  gases  are  liberated  from  them ; 
this  causes  the  particles  to  rise  to  the  top,  or,  if  the  gases  are  not 
liberated  with  sufficient  rapidity,  they  may  drop  to  the  bottom,  and 
either  at  the  top  or  bottom  the  remains  of  these  suspended  parti- 
cles, consisting  of  the  more  refractory  portions,  together  with 
fibrous  and  cellulose  matter  which  are  undergoing  this  process  of 


142  Alvord — Sewage  Purification  Plants. 

dissolution,  form  a  coat  of  matter,  and,  as  Prof.  Talbot  has  pointed 
out,  it  is  desirable  that  there  should  be  a  large  surface,  so  that 
these  particles  may  be  as  thoroughly  dissolved  as  possible  before 
they  become  covered  by  other  particles. 

With  reference  to  the  Professor's  allusions  to  our  different  ideas 
about  the  "fermentation  period,"  I  may  say  that  it  seems  to  me  it  is 
largely  a  distinction  without  a  serious  difference.  As  I  under- 
stand it.  he  thinks  the  area  of  this  matte  and  the  size  of  the  tank 
are  the  vital  questions — that  they  should  be  sufficiently  ample  so 
that  the  suspended  matter  should  not  cover  them  too  rapidly,  while 
my  idea  is  that  the  particles  of  suspended  matter  entering  the  tank 
must  remain  within  the  tank  a  period  which  I  term  the  "fermenta- 
tion period,"  during  which  they  must  be  dissolved  into  their  con- 
stituent gases  or  reduced  into  solution.  I  do  not  see  very  much 
difference,  myself,  between  the  two  theories,  but  if  there  is  any, 
we  will  have  to  work  it  out  together. 

Prof.  Talbot — I  did  not  intend  to  attach  any  special  importance 
to  the  calculation  of  this  area,  especially  as  with  the  usual  depth  of 
tank  its  capacity  will  be  proportional  to  this  area.  As  Mr.  Alvord 
has  just  expressed  himself,  I  should  want  to  express  myself  as  not 
agreeing  that  the  time  period  of  the  passage  of  the  sewage  through 
the  tank  is  equal  to  the  actual  period  of  fermentation.  In  fact,  I 
have  shut  off  the  flow  entirely  from  an  overdosed  septic  tank  in 
order  to  get  rid  of  accumulated  organic  matter,  and  after  a  week 
have  found  the  condition  of  the  tank  materially  different  from 
what  it  was  at  the  beginning.  Evidently  the  period  of  passing 
through  the  tank  may  not  be  the  period  required  for  bacterial  re- 
duction. My  objection  to  the  use  of  the  term  is  that  it  may  lead 
one  to  suppose  that  this  period  is  the  time  which  the  sewage  re- 
mains in  the  tank,  and  that  it  is  identical  with  the  fermentation 
period. 

Mr.  Finley — Would  it  not  be  the  case  that  a  small  tank,  which 
we  will  say  takes  a  large  volume  of  flow,  would  naturally  fill  with 
these  undecomposed  particles  of  suspended  matter,  while  a  tank 
which  might  be  very  ample  in  capacity  would  not  be  satisfactory  ? 

Prof.  Talbot — It  is  not  a  question  whether  enough  area  or  capac- 
ity is  being  used,  but  what  term  should  be  used  to  describe  the  ratio 
between  the  capacity  of  the  tank  and  the  number  of  hours'  flow  of 
the  sewage  going  through  the  tank. 

Mr.  Alvord — We  have  been  driven  into  this  theory  largely  be- 
cause tanks  which  seemed  to  be  too  small  filled  up,  and  also 
tanks  which  seemed  to  be  too  large  filled  up.  By  partition- 
ing off  those  tanks  which  were  too  large  we  get  a  capacity  from 
which  the  surface  matte  remains  only  four  or  five  inches  thick. 
There  is  no  further  accumulation.  Now  there  seems  to  be  an  ad- 


Alvord — Sewage  Purification  Plants.  145 

justment  here  between  the  amount  of  particles  which  entered  with 
the  flow  and  were  fermented  and  the  capacity  of  the  tank,  and  I 
have  unfortunately  selected  "  fermentation  period  "  as  describing 
that  ratio.  May  I  ask  the  professor  what  term  he  would  prefer  ? 

Prof.  Talbot — Let  me  say  first  that  I  am  not  disagreeing  with 
Mr.  Alvord's  statement  that  a  suitable  size  of  tank  should  be  used. 
I  have  no  term  to  propose  other  than  to  state  the  capacity  of  the 
tank  in  terms  of  the  number  of  hours'  flow,  viz.:  instead  of  eight 
hours  of  "rest  period"  or  "fermentation  period,"  use  "the  cubic 
capacity  of  the  tank  equals  eight  hours'  flow  of  sewage." 

Mr.  W.  G.  Potter  (by  letter)— In.  the  discussion  of  Mr.  Alvord's 
paper  on  Sewage  Purification,  the  question  of  the  effect  of  cold 
weather  upon  the  septic  method  of  purification,  and  of  possible 
freezing  of  the  liquid,  was  touched  upon. 

In  regard  to  the  latter  point  I  wish  to  submit  the  following: 

It  is  a  fact  self  evident  to  all  that  chemical  action  of  any  kind  de- 
velopes  or  causes  heat.  Chemical  action  of  course  is  progressing 
in  the  septic  tank,  in  the  contact  beds  and  in  the  sand  beds,  and  ex- 
periments show  that  the  heat  produced  in  the  septic  action  is  suffi- 
cient to  keep  the  temperature  throughout  about  the  same  and  is 
often  sufficient  to  raise  the  temperature  of  the  effluent  higher  than 
the  original  sewage. 

In  the  report  of  the  Massachusetts  State  Board  of  Health  for 
1898  in  coke  filter  bed  No.  103,  which  was  used  for  the  full  twelve 
months,  the  entering  sewage  had  an  average  temperature  of  58  de- 
grees and  the  effluent  59  degrees. 

In  sand  bed  No.  1 16  of  same  report,  the  use  of  the  bed  was  be- 
gun in  September,  with  a  loss  of  temperature  for  several  weeks 
while  nitrification  was  not  in  full  operation,  but  the  whole  period 
from  September  to  January  showed  a  gain  of  I  degree  in  temperature. 

In  1 899  report  of  same  authorities  in  septic  tank  with  the  record  of 
ten  months  from  March  ist  to  January  ist,  the  temperature  showed 
an  average  gain  of  1.2  degrees  for  the  entire  period.  The  lowest 
monthly  average  temperature  of  original  sewage  was  46  degrees, 
while  the  lowest  for  septic  tank  effluent  was  48  degrees  Fah. 

In  1900  report  the  septic  tank  again  shows  a  gain  of  i  degree 
for  the  yearly  average,  the  lowest  average  temperature  (for  any  one 
month)  of  original  sewage  being  39  degrees  in  February  and  De- 
cember, with  temperature  of  effluent  raised  to  43  degrees  and  47 
degrees  respectively  for  same  months. 

Other  experiments  by  the  same  authorities  show  the  same  results, 
with  some  cases  of  a  slight  fall  in  temperature. 

In  the  Wauwatosa  plant  described  in  Mr.  Alvord's  paper,  tem- 
peratures were  taken  during  the  cold  spell  of  December,  1901,  with 
the  following  results :  Temperature  of  air  outside,  about-4  degrees 


144  Alvord — Seivage  Purification  Plants. 

Fah.;  original  sewage  entering  septic  tank  48  degrees,  in  the  con- 
trolling chamber  between  septic  tank  and  sand  beds  47  degrees,  and 
entering  creek  at  final  outlet  44  degrees ;  a  total  loss  of  4  degrees 
in  extremely  cold  weather. 

Therefore  it  seems  to  the  writer  beyond  question,  that  no  fear 
need  be  entertained  of  any  serious  trouble  in  operation  of  the  sep- 
tic purification  plant  due  to  cold  weather  in  this  climate.  There  is 
no  doubt  but  that  cold  weather  makes  bacterial  action  more  slug- 
gish, but  at  the  temperatures  above  shown  the  action  will  still  con- 
tinue at  a  rate  sufficient  for  good  purification. 


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